Device for producing single crystals

ABSTRACT

PCT No. PCT/JP94/00821 Sec. 371 Date Nov. 27, 1995 Sec. 102(e) Date Nov. 27, 1995 PCT Filed May 23, 1994 PCT Pub. No. WO94/28206 PCT Pub. Date Dec. 8, 1994A device for producing single crystals has been presented which enables the pulling up and growing of single crystals. Without loss of accurate control of the oxygen concentration in the crystal, and with excellent dielectric strength of subsequently produced gate oxide films. A heat resistant and heat insulating component (7) of cylindrical or cylinder-like form surrounding the pulling up zone of the single crystal is suspended from the ceiling (6a) or the upper part of the wall of the metallic vessel (6) with a gap (h1) from the ceiling to divide the inert gas (30) supplied from above into inert gas flows (33 and 32) outside and inside this component.

TECHNICAL FIELD

The present invention relates to a device and a process for producingsingle crystals of silicon (and similar materials) having littlecontamination or thermal oxidation induced stacking faults, thusenabling the production of wafers whose gate oxide films have excellentdielectric strength. This device and process are also suited for finelycontrolling the oxygen content of the pulled crystal.

BACKGROUND ART

Single crystals that are produced in according to the Czochralskiprocess contain appreciable amount of oxygen, which has been melted outof the quartz (SiO₂) crucible, as the silicon melt reacts with thequartz crucible. consequently, during repetitive heat treatment whichoccurs in the IC and LSI manufacturing processes, this oxygen tends toprevent the occurrence of slips and burrs. Furthermore, during the heattreatments at a temperature of approximately 1000° C., oxideprecipitates in the crystal aggregate to form stacking faults of highdensity and reduce the impurities in the surface layers of wafers cutfrom the crystal (a phenomenon known as intrinsic gettering).

FIG. 6 schematically illustrates a cross section of a current device andthe pulling-process according to the Czochralski technique. The crucible1 is comprised of a quartz vessel 1a on the inside and a graphite vessel1b on the outside. A heating element 2 is mounted outside the crucible1, in which the melt 5, the charge material for the crystal melted bythe heating element, is contained. A seed crystal 3 is lowered until itmakes contact with the surface of the melt 5 and then is pulled upwardto grow a crystal at its lower end. These parts and components arecontained in a metallic vessel provided with a water cooling device, allof which constitutes a whole device for producing single crystals.

During the course of the single crystal pulling process, inert gas (suchas argon gas) of high purity is introduced into the metallic vessel 6from above at the center, forming a gas flow 30. The gas flow 30 turnsinto a gas flow 31 containing both silicon monoxide (SiO) that hasevaporated from the surface of the silicon melt 5 and carbon monoxide(CO) generated as a result of the silicon monoxide reacting at hightemperatures with the graphite components such as the heating element 2,the graphite vessel 1b, etc. The gas flow 31 flows down along theoutside and the inside of the heating element 2 to be discharged throughthe discharge ports 8.

Since the argon gas flow 31 in the metallic vessel 6 is turbulent andlocally stagnant, silicon monoxide is deposited on the ceiling of thevessel 6 layer by layer or in particle forms. Fine particles or smallblocks of the deposited silicon monoxide fall onto the surface of themelt 5, are incorporated in the boundary layer of the growing crystaland give rise to dislocations in crystal.

Another problem is that, the silicon melt is contaminated also, unlesscarbon monoxide is properly discharged. That is, the carbon monoxideincorporates into the single crystal, will induce lattice defects in thesingle crystal.

In order to effectively obviate these problems, two devices mentionedbelow has been proposed.

FIG. 4 illustrates schematically a pulling assembly (the first device)proposed by the U.S. Pat. No. 4,330,362: Kokoku No. 57-40119. Thisdevice is characterized by having an upper flat annular rim 7aprojecting beyond the crucible edge and a joining piece 7b attached tothis annular rim 7a and extending downwardly and cortically from itsinner edge, the joining piece 7b being 0.2 to 1.2 times as high as thecrucible 1.

FIG. 5. illustrates schematically another pulling assembly (the seconddevice) disclosed in Kokai No. 64-72984. This device is characterized byhaving a heat resistant and heat insulating cylinder 10 that extendsdownward coaxially surrounding the single crystal 4 being pulled and istightly joined to the subvessel 6c at its junction with the metallicvessel 6. The device is also characterized by having a heat resistantand heat insulating annular plate 11, which closely rests on the upperend of the heat insulating component 12 and has an outside diameternearly identical with that of the heat insulating component 12, theinside diameter of which tightly fits the above mentioned heat resistantand heat insulating cylinder 10.

The first and the second devices as mentioned above effectively increasethe pulling rate by shielding the crystal pulled from heat irradiationand they prevent fine particles of silicon monoxide from falling intothe melt, and suppress generation of the thermal oxidation inducedstacking faults (OSF). However, these devices do not solve the problemsof enhancing the dielectric strength of the oxide films of the waferswhich are cut from the crystal. And without improved the dielectricstrength, it is impossible to produce small highly integratedsemiconductor. In addition, these devices can not solve the problem ofhaving an adverse effect on controlling the oxygen concentration in thecrystal.

The exact mechanism of formation of faults, which that deteriorate thedielectric strength of the oxide films has not yet been clarified. Ithas been reported that the cores of faults in crystals, which constitutethe origin of the defects in the dielectric strength of the oxide filmsare formed during the crystal growth, the cores being contracting at thehigh temperature stage (above 1250° C.) and grown at the low temperaturestage (below 1100° C.) (See 30P-ZD-17. The Japan Society of AppliedPhysics Extended Abstracts, The 39th Spring Meeting, 1992). In short,the dielectric strength of the oxide films are known to depend on thethermal history immediately after crystal pulling.

In the first device as schematically illustrated in FIG. 4, the internalclearance of the circular truncated cone 7b located surrounding thecrystal being pulled is as low as 0.2 to 1.2 times that of the crucible.Thus immediately after crystal grows it is exposed to the lowtemperature atmosphere in the metallic vessel, and is cooled too rapidlyto facilitate shrinkage of the defect cores. As the result thedielectric strength of the oxide films deposited on the wafers cut fromthe crystal is deteriorated.

In the second device as schematically illustrated in FIG. 5, since theheat resistant and heat insulating cylinder 10 is tightly joined to thewater cooled metallic vessel 6 and the subvessel 6c at their junction,the internal surface of the heat resistant and heat insulating cylinder10 is cooled by thermal conduction, a rapid cooling takes place at thehigh temperature stage immediately after crystal growing. Hence,immediately after the crystal grows only a slight shrinkage of thedefect clusters occurs and as a result the dielectric strength of theoxide films are deteriorated.

While the oxygen concentration in the single crystal is required to bebrought under control to the accuracy of ±0.75×10¹⁷ atoms/cm³ from thetarget value in order to effectively carry out gettering action aboutoxygen in the single crystals as mentioned before, it is stronglyinfluenced by the state of the above mentioned argon gas flow.

The flow velocity of the argon gas (Vg) depends on the gas supplypressure (Pg), the gas flow rate (Qg), the gas passage cross section(Ag) and the internal furnace pressure (Pf). This relationship can bedescribed by the formula (A) given below.

    Vg=(Qg/Ag)×(Pg/Pf)                                   (A)

This gas flow velocity (Vg) significantly influences the contaminationof the single crystals by the silicon monoxide that evaporates from thesurface of the melt.

Since in the first device illustrated in FIG. 4, the circular truncatedcone 7b, the flat annular rim 7a, and the circular cylinder 18 aretightly connected to each other, the entire argon gas flow from theupper side of the pulling chamber forms a gas flow 31 that passes insidethe joining piece 7b to the narrow gap between the bottom portion of thejoining piece 7b and the surface of the melt 5, after which it flowsdownward along the inside and the outside surfaces of the heater 2.

Since, as mentioned before, the argon gas flow from the pulling chamberis turbulent, the influence of the upward flow of the silicon monoxidethat evaporates from the surface of the meIt 5 upon the argon gas flowis not uniform along the circumference of the joining piece 7b. Hencethe outward flow of the argon gas at the lower end of the joining piece7b is not circumferentially uniform, rather there is variation in thevelocity of the the argon gas flow (Vg) between the lower end of thejoining piece 7b and the surface of the melt 5 depending on the locationalong the circumference of the joining piece 7b.

When, in the first device shown in FIG. 4, the argon gas flow rate (Qg)is enhanced and the gas flow velocity (Vg) is increased, sufficientdischarge of the silicon monoxide and the carbon monoxide can beobtained, thus preventing them from contaminating. However, since, theflow velocity (Vg) in the gap between the end of the joining piece 7band the surface of the melt 5 subsequently increases, the localvariation of the flow velocity increases, depending on thecircumferential position. And variation in the surface temperature andthe convection in the melt 5 is induced, making it difficult to controlthe oxygen concentration in the crystal within a certain range withdesirable accuracy and reproducibility.

As the flow velocity (Vg) in the gap between the lower end of thejoining piece 7b and the surface of the melt 5 increases, the surface ofthe melt 5 tends to vibrate, leading to a situation where it isimpracticable to carry out drawing a dislocation free single crystal.

On the other hand, when the argon gas flow rate (Qg) is reduced and thegas flow velocity (Vg) is lowered, the variation in the flow velocity(Vg) in the gap between the lower end of the joining piece 7b and thesurface of the melt 5 decreases, hence control over the oxygenconcentration is improved. However, decrease in the gas flow velocity(Vg) entails a certain loss in capability to discharge silicon monoxideand carbon monoxide, raising the problem of contamination of the siliconmelt 5 by silicon monoxide and carbon monoxide particles.

The problem mentioned above exists not only with the first device butalso with the second device illustrated in FIG. 5, and is a problemcommon to existing devices. In short. with existing devices there aredifficulties in providing the dielectric strength of the oxide films forthe highly integrated micro-semiconductor or in accurately controllingthe oxygen concentration in the crystal.

DISCLOSURE OF THE INVENTION

The present invention aims to provide a device and a process thatenables production of single crystals from which wafers whose oxidefilms are superior in the dielectric strength can be produce. This isaccomplished by a pulling up technique by which an adequate temperaturedistribution in the direction of withdrawing the single crystal isformed, contamination of the single crystal is avoided, and the accuratecontrol of the oxygen concentration in the single crystal is maintained.

The aims of this invention are achieved by providing (1) the device forproducing single crystals of silicon as described below and (2) themethod as described below for producing single crystals by the use ofthis device.

(1) FIG. 1 illustrates the device for producing the single crystals. Thedevice is characterized by and comprising: the crucible 1 which containsthe melt 5, of the charge material for the single crystal to be grown,the heating element 2 to heat the melt 5, the withdrawing measure 9 togrow the single crystal 4 after bringing the seed crystal 3 into contactwith the melt 5, and a metallic vessel 6 which contains all of theconstituents described above, wherein there are arranged a heatresistant and heat insulating component 7 in a cylinder form or in aconical form with the diameter being narrowed gradually in the top tobottom direction, the component surrounding the periphery of the zone ofpulling up the single crystal, and supporting means 21, 22 of the heatresistant and heat insulating component, being capable of adjusting thegap h₁ between the upper top of the component 7 and the ceiling part 6aof the metallic chamber 6, through which gap h1 inert gas supplied fromthe upper part of the metallic chamber 6 can be branched into inert gas33 flowing down inside the component 7 and inert gas 32 flowing downoutside the component 7.

(2). A method for producing a single crystal, using a device forproducing a single crystal, the device comprising crucible 1 for placingmelt 5 of the raw materials of the single crystal to be grown, heatingmeans 2 for heating the melt 5, pulling-up means 9 for growing thesingle crystal by making seed crystal 3 in contact to the surface of themelt 5 in the crucible 1, and metallic chamber 6 For placing theindividual means, wherein a heat resistant and heat insulating component7 in a cylinder form or in a conical form with the diameter beingnarrowed gradually in the top to bottom direction, is placed above themelt in the crucible by means of height-adjustable supporting means 21,22 of the heat resistant and heat insulating means, and gap h₁ isarranged between the upper top of the component 7 and the ceiling part6a of the metallic chamber 6, through which gap h₁ inert gas suppliedfrom the upper part of the metallic chamber 6 can be branched into inertgas 33 flowing down inside the component 7 and inert gas 32 flowing downoutside the component 7 to subsequently meet the branched flows of theinert gas together.

Preferably, the heat resistant and heat insulating component 7 describedabove in (1) and (2) is made of graphite, having the surface thereofcoated with silicon carbide. The gap h₁ between the upper top of thecomponent 7 and the ceiling part 6a of the metallic chamber 6 can beadjusted within a range of 5 mm to 100 mm, so as to adjust the flow,namely the flow rate of the inert gas flowing into the gap. The gap h₁is adjusted by means of the supporting means 21, 22 of the heatresistant and heat insulating component placed on the ceiling part ofthe metallic chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the device in accordance with the presentinvention; (a) showing a cross sectional view of the device;

FIG. 2 is an illustration of an example of one way to support the heatresistant and heat insulating part; (a) being a side view section, (b)being a top view, and (c) being a bird's-eye view from the top and toone side;

FIG. 3 is an illustration of another example of a way to support theheat resistant and heat insulating component; (a) being a side viewsection, (b) being a bird's-eye view of the supporting legs, and (c)being a bird's-eye view of the heat resistant and heat insulatingcomponent supported by the supporting legs;

FIG. 4 is a side view section of an example of a conventional device forproducing single crystals;

FIG. 5 is a side view section of another example of a conventionaldevice for producing single crystals; and

FIG. 6 is a schematic cross section illustrating a device and processfor producing a single crystal in accordance with the Czochralskiprocess.

BEST MODE FOR CARRYING OUT THE INVENTION

The device and the process in accordance with this invention areexplained referring to figures below.

FIG. 1 is an illustration of the device in accordance with thisinvention, (a) showing a cross section of the device, and (b) showing anenlarged view of the key portion. The crucible 1 is illustrated in FIG.1(a), and consists of a dual structure in which the inside is a quartzvessel 1a, and the outside is a graphite vessel 1b which are placed onthe crucible supporting shaft 1c. This crucible supporting shaft 1c ismade in such way that it may be rotated and raised or lowered inaddition to supporting the crucible.

In FIG. 1, the metallic vessel 6 provided with a water cooling device,is a cylindrical vacuum chamber consisting of the ceiling 6a and theside wall 6b provided with a shaft for withdrawing of a single crystalaligned with the center line, the crucible 1 being positioned in itsmiddle and surrounded by a heater 2. Above the crucible 1, a withdrawingmeasure 9 that can be turned around and raised or lowered is suspendedfrom the center of the ceiling 6a of the metallic vessel, and a seedcrystal 3 is placed at its lower end. The seed crystal 3 is pulled up asit is turned around by the withdrawing measure 9, and a single crystal 4is grown at its lower tip where it makes contact with the melt 5.

As is illustrated in FIG. 1(b), heat insulating component 7 in a conicalshape is sustained, coaxially with the pulling-up means 9, in theperiphery of the zone of pulling up the single crystal, in a manner suchthat the component 7 might not be in contact to the ceiling part 6a ofthe metallic chamber 6 while keeping gap h1 between the upper top of theheat resistant and heat insulating component 7 and the ceiling part 6ain order that the inert gas, namely argon gas, can flow through the gapwhile keeping gap h_(z) from the surface of the melt 5.

FIG. 2 depicts a view wherein the heat resistant and heat insulatingcomponent 7 is sustained by means of supporting member 21 as oneembodiment of the supporting means of the heat resistant and heatinsulating means. FIG. 2(a) depicts a longitudinal cross section of thesustaining state by means of the supporting member 21: FIG. 2(b) depictsa horizontal cross section in a top view line A--A. Furthermore, FIG.2(c) depicts a perspective view of the heat resistant and heatinsulating component 7. In this embodiment, four square bars as thesupporting member 21 are mounted at an interval of 90° angle on theceiling part 6a of the metallic chamber 6, and the upper top of the heatresistant and heat insulating component 7 is held tightly by means ofthe supporting member 21 and tying bolts 21a. The heat resistant andheat insulating component 7 is thereby sustained, so that the upper topof the heat resistant and heat insulating component 7 might not comeinto contact to the ceiling part 6a while keeping the gap for argon gasto be branched and subsequently flow downward inside and outside theheat resistant and heat insulating component 7. The number of thesupporting member 21 is not limited to the aforementioned numericalfigure 4: the shape thereof is not limited to a square bar shape.

As shown in FIG. 2(c), a plurality of sustaining through-holes 7c forreceiving the bolts 21a are arranged on the upper top part of the heatresistant and heat insulating component 7. This is because by selectingappropriate through-holes for sustaining, the gap (the aforementioned"h₁ ") between the upper top of the heat resistant and heat insulatingcomponent 7 and the ceiling part 6a can be adjusted. Thus, the adjustingmeans is not limited to the means illustrated.

FIG. 3 depicts a view where the heat resistant and heat insulating means7 is sustained by means of supporting leg member 22 as anotherembodiment of the supporting means of the heat resistant and heatinsulating means: the heat resistant and heat insulating means 7 ismounted on the upper part of the side wall 6b of the metallic chamber 6.FIG. 3(a) depicts a longitudinal cross section of the supporting stateby means of the supporting leg member 22; FIG. 3 (b) depicts abird's-eye view of the supporting leg 22, wherein the supporting legmember 22 is composed of the upper end ring 22a and four sets ofsupporting leg 22b mounted thereon and end tips 22c. Further, FIG. 3(c)depicts a bird's-eye view of the heat resistant and heat insulatingcomponent 7 supported by means of the supporting leg member 22, whereinprotrusions are placed at 4 positions along the circumference of theupper top face thereof.

In this embodiment, the supporting leg member 22 is held by setting theupper end ring 22a of the supporting leg member 22 into a retaining ring23 arranged on the upper part of the side wall 6b of the metallicchamber 6. By subsequently hooking the protrusions 7d of the heatresistant and heat insulating component 7 onto the end tips 22c of thesupporting leg member 22, the heat resistant and heat insulatingcomponent 7 is sustained in position at a distance from the ceiling part6a. Additionally, the gap (h₁) between the upper top of the heatresistant and heat insulating component 7 and the ceiling part 6a isadjusted by the adjustment of the length and angle of the supporting leg22b of the supporting leg member 22. As in FIG. 2, the shape of thesupporting leg member 22 and the number of the supporting leg 22b arenot limited to those illustrated.

As apparently shown in FIGS. 2 and 8, the structure of the supportingmeans should be the one which does not close the gap between the uppertop of the heat resistant and heat insulating component 7 and theceiling part 6a. The gap between the upper top of the heat resistant andheat insulating component 7 and the ceiling part 6a is arranged so as tobranch the argon gas flow fed from the upper part of the metallicchamber 6 into the downward flow in the inside region of the heatresistant and heat insulating component 7 and the downward flow in theoutside region of the heat resistant and heat insulating component 7. Bysupporting the heat resistant and heat insulating component 7 via theceiling part 6a and side wall 6b of the metallic chamber 6 by using suchsupporting means, the objective of the present invention can beattained.

In any of the embodiments, the heat resistant and heat insulatingcomponent 7 should be made of graphite, and the shape should he in theform of a cylinder or a conical form with the diameter being narrowedgradually in the top to bottom direction, and preferably, the surfacethereof is coated with silicon carbide. The reason why the heatresistant and heat insulating component 7 should be made of graphite isbecause the pull-up crystal can be made with high purity, and with asmaller risk of contaminating the crystal due to heavy metals. When thesurface is coated with silicon carbide, furthermore, gas discharge fromthe air holes of the graphite component is prevented, also preventingthe reaction of silicon monoxide vaporized from the surface of the melt5 with the graphite component.

In order to produce a single crystal of good dielectric strength of theoxide films, it is necessary to adequately control the cooling rate inthe pulled-up crystal, in particular to have adequate control of thecooling rate of crystal at the high temperature stage immediately aftergrowing the crystal. Therefore, in the device and the process inaccordance with this invention the heat resistant and heat insulatingcomponent 7 is extended in a wide range around the withdrawing rangefrom the surface of the melt 5 in the crucible to the ceiling 6a of themetallic vessel 6. In addition the heat resistant and heat insulatingcomponent 7 is installed with an adequate gap between itself and theceiling 6a of the water cooled metallic vessel 6 and is not tightlyjointed to the ceiling.

Compared with the low internal height of the connection 7b as in thedevice shown in FIG. 4, as a result of this structure, immediately aftercrystal growing the crystal is not directly exposed to the lowtemperature atmosphere.

Compared with the device illustrated in FIG. 5 where the heat resistantand heat resistant and heat insulating component 10 is closely connectedto the ceiling of the metallic vessel 6, temperature decrease due tothermal conduction is prevented, therefore the inside surface of theheat resistant and heat insulating component 7 also can be maintained athigher temperature. Hence the device and the process in accordance withthis invention enable reduction of the cooling rate immediately aftercrystal growing, to cool the single crystal slowly at the hightemperature stage above 1100° C., and to improve the dielectric strengthof subsequently produce gate oxide films.

As is illustrated in FIG. 1(a), the flow of argon gas 30 supplied fromthe upper part of the metallic vessel 6 is divided into a gas flow 33flowing down inside the heat resistant and heat insulating component 7and into another gas flow 32 flowing down outside the heat resistant andheat insulating component 7 out of the gap between the upper end of theheat resistant and heat insulating component 7 and the ceiling 6a. Thedivided gas flow 32 and 33 rejoin to form a gas flow 34 which flowsbetween the crucible 1 and the heater 2 and outside the heater 2 to bedischarged along with silicon monoxide and carbon monoxide through thedischarge port 8. Therefore, ever if the gas flow velocity is reduced bydiminishing the rate of gas flow 33 in order to limit the localdifference in the flow velocity generated in the argon flow between thelower end of the heat resistant and heat insulating component 7 and thesurface of the melt 5, the flow velocity beyond a certain value for theconfluence of gas 34 toward the discharge port 8 can be secured, as longas a sufficient rate of the downward gas flow 32 outside the heatresistant and heat insulating component 7 is maintained. Consequentlyboth, the oxygen concentration in the crystal can be controlled withhigh degree of accuracy and the silicon monoxide and carbon monoxide canbe adequately discharged.

The gap (h₁) between the upper edge of the heat resistant and heatinsulating component 7 and the ceiling 6a is preferably set in the rangefront 5 mm to 100 mm. For h₁ less than 5 mm the gas flow 33 becomesdominant and the local variation in the flow of the argon gas betweenthe lower end of the heat resistant and heat insulating component 7 andthe surface of the melt 5 increases, generating variation in the surfacetemperature of the melt 5 and the convection of the melt 5, thus makingit hard to precisely control the oxygen concentration in the crystal.For h₁ larger than 100 mm on the other hand, influenced by the watercooled metallic vessel 6, the cooling rate of the pulled-up crystal 4 istoo rapid and the dielectric strength of subsequently produce gate oxidefilms deteriorates. Furthermore, the desirable setting for h₁ is lessthan 30 mm. With h₁ greater 30 mm, the gas flow 33 flowing to thedischarge port 8 becomes reversed or stagnant, and a part of theevaporated silicon monoxide is deposited in the metallic vessel 6 whereit might fall into the melt 5.

The gap (h₂) between the lower edge of the heat resistant and heatinsulating component 7 and the surface of the melt 5 is preferablybetween 10 mm and 50 mm. For h_(z) larger than 50 mm, the crystalpulling rate has to be reduced, because the influence upon the crystalof the thermal radiation from the heater and the melt becomes excessive.With h₂ in the range between 10 and 50 mm, the flow of argon gas betweenthe lower edge of the heat resistant and heat insulating component 7 andthe surface of the melt 5 is uniform, and also the heat insulatingeffect upon the pulled crystal is secured.

As mentioned above, it is essential to minimize the local fluctuation inthe velocity of the argon gas flow above the surface of the melt 5 inorder to accurately control the oxygen concentration in the crystalwithin ±0.75×10¹⁷ atoms/cm⁸. Continuous control of the gas flow velocityis realized by adjusting the gap h₁ between the upper end of the heatresistant and heat insulating component 7 and the ceiling 6a and byadjusting the gap h₂ between the lower end of the heat resistant andheat insulating component 7 and the surface of the melt 5.

Prior to processing a single crystal in the device in accordance withthis invention, first the gaps h₁ and h₂ are to be set to deliver theappropriate flow velocity and rate of flow, depending on the dimensions,the pulling rate the required oxygen concentration in the crystal andother process conditions, and then the production of the single crystalis to be carried out.

A preferable embodiment of this invention is described above, In theparagraphs below the effects of this invention are described.

In a manufacturing device assembled in accordance with this invention asillustrated in FIG. 1(a) and (b), the heat resistant and heat insulatingcomponent 7 is made of a circular truncated cone with a height of 380mm, an inside diameter of 400 mm at the upper end, an inside diameter of200 mm at the lower end, and a thickness of 10 mm. In FIG. 2(a) theupper end of the heat resistant and heat insulating component 7 and theceiling 6a of the metallic vessel 6 are separated by a gap h₁ of 10 mm,and the lower end of the heat resistant and heat insulating component 7and the surface of the melt 5 are separated by a gap h₂ of 30 mmsupported with the supporting legs 21 nearly concentrically with thewithdrawing shaft 9 of the single crystal.

The material of the heat resistant and heat insulating component 7 wasgraphite and its surface was coated with silicon carbide.

The pulled up crystals 4 were silicon single crystals 6 inches indiameter, the silica crucible 1a used was 406 mm (16 inches) indiameter, the rate of argon gas flow into the metallic vessel 6 was setat 60 liter/min. the rate of pulling up was 1.1 mm/min. and the lengthof the pulled crystals was 1200 mm. For the purpose of comparison, othersample crystals were pulled up in the device illustrated in FIG. 4 (thefirst device) under the same conditions.

The single crystal products were evaluated in terms of; the yield ratioof dislocation free single crystals; the OSF acceptance ratio; thedielectric strength of gate oxide films acceptance ratio; and the oxygenconcentration acceptance ratio. In this demonstration the yield ratio ofthe dislocation-free single crystals was represented by the ratio of theweight of the dislocation-free single crystal after excision of theportion with dislocation, to the weight of the original chargedpolycrystalline material.

The OSF acceptance ratio was represented by the ratio of the number ofwafers of acceptable OSF to the total numbers of wafers, with thecriteria of acceptance to be less than the standard number of OSFdefects (10 defects/cm³) after cutting silicon wafers out, and puttingthem through heat treatment of 780° C. for 3 Hr. and 1000° C. for 16 Hr.followed by selective etching. The acceptance ratio of the dielectricstrength of gate oxide films was evaluated in terms of the voltageramping procedure with a gate electrode consisting of phosphorus(P)-doped polycrystalline silicon with a 250 Å thick dry oxide film andan area of 8 mm². The criteria for acceptance was to withstanddielectric strength above the standard value (8 MV/cm of the meanelectric field) before an avalanche. The result was represented by theratio or the number of acceptable wafers to the total number of waferstested.

In addition, single crystals pulled up free from dislocation and withoxygen content within ±0.75×10¹⁷ atoms/cm³ were determined to be ofacceptable oxygen content, and the ratio of acceptance is represented bythe ratio of the weight of the single crystals of acceptable oxygencontent to the weight of dislocation free single crystals.

For these tests, a total of 34 crystals ware pulled up using thisinvention and, for comparison, the device illustrated in FIG. 4 (thefirst device). The results of above tests are shown in Table 1:

                  TABLE 1                                                         ______________________________________                                                    Results in Acceptance                                                                         Results by Tests                                  Test Items  with This Invention                                                                           for Comparison                                    ______________________________________                                        Yield Ratio,                                                                              78.3%           77.8%                                             Dislocation Free                                                              Single Crystals                                                               OSF         98.6%           92.1%                                             Acceptance                                                                    Ratio                                                                         Acceptance Ratio,                                                                         86.5%           51.8%                                             Dielectric Strength                                                           of Gate Oxide Films                                                           Acceptance Ratio,                                                                         96.0%           83.9%                                             Oxygen                                                                        Content                                                                       ______________________________________                                    

It can be seen that, all the test results for single crystals preparedwith the device and by the process in accordance with this inventiondemonstrate better characteristics than those of the products forcomparison, and a particularly remarkable difference can be seen in theacceptance ratio of the dielectric strength of gate oxide films.

APPLICABILITY FOR INDUSTRIAL USE

In accordance with this invention, it is possible to both divide and tocontrol confluence of the gas flow, further more it is possible tocontrol the cooling rate of the crystal in the direction of withdrawingthe single crystal.

By these means intrusion of contaminants into the single crystal can beprevented and improvement of dielectric strength of the gate oxide filmsproduced from the single crystal as well as precise control of theoxygen concentration in the crystal can be attained. Therefore thisinvention is applicable in metal fabrication and semiconductorindustries as a device and a process for producing single crystals.

What is claimed is:
 1. A device for producing a single crystal, comprising:a crucible for placing a melt of raw materials of a single crystal to be grown; heating means for heating the melt; pulling-up means for growing the single crystal by placing a seed crystal in contact to the surface of the melt in the crucible; and a metallic chamber for placing said individual means, wherein there are arranged a heat resistant and heat insulating component in a cylinder form or in a conical form with the diameter being narrowed gradually from the top to bottom direction, a component surrounding the periphery of a zone of pulling up the crystal, and supporting means of the heat resistant and heat insulating means, being capable of adjusting a gap between an upper top of the component and a ceiling part of the metallic chamber, through which gap an inert gas supplied from the upper part of the metallic chamber can be branched into inert gas flow flowing down inside the component and inert gas flow flowing down outside the component.
 2. A device for producing a single crystal according to claim 1, wherein a supporting means of the heat resistant and heat insulating component is arranged on the ceiling part of the metallic chamber and the gap between the upper top of the heat resistant and heat insulating component and the ceiling part of the metallic chamber is adjustable structurally.
 3. A device for producing a single crystal according to claim 1 or claim 2, wherein the gap between the upper top of the heat resistant and heat insulating component and the ceiling part of the metallic chamber is 5 mm to 100 mm.
 4. A device for producing a single crystal according to claim 1 or claim 2 wherein the heat resistant and heat insulating component is made of graphite and the surface thereof is coated with silicon carbide. 